Old Roto-Matic furnace questions.

Discussion in 'Furnaces and their construction' started by Brendon Hartley, Jan 26, 2020.

  1. image.jpg image.jpg image.jpg image.jpg

    Hello, this is my first time posting, forgive me if this has been asked before but I’m unable to find any answers.

    I have an old gas furnace made by the Roto-Matic Company Limited in Saskatoon Canada. It has a design I’m unfamiliar with (see images) the lid is solid without vent and down low in the furnace is a passage to the outside. This came out of a high school and was being used for introductory aluminum casting apparently.

    is someone able to explain the design and use of a furnace like this? It seems there would be a great deal of heat directed right at the gas and blower controls.

  2. PatJ

    PatJ Silver

    Do you have a photo of the lid?
    And a photo looking down into the furnace?

    Need more photos from all sides too.

  3. PatJ

    PatJ Silver

    My guesses:

    1. The box on the side is the exhaust, which connects to a vertical exhaust pipe/chimney (not shown).
    2. Burner tubes go into the furnace low on the right side.
    3. Pipe with coupling (union) on it is input from a natural gas supply.
    4. Box with hinged cover is the flame sensor.
    5. Vertical pipe on left side, ?
    Last edited: Jan 26, 2020
  4. OMM

    OMM Silver

    That looks like a very interesting design. It looks like the exhaust is coming off the side and going into an afterburner, Which then leads to a exhaust.
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    here’s a few more photos, the gas goes trough a on/off valve, through a regulator, a pilot valve, then through some sort of electronic valve which I assume is designed to shut off gas flow in the case of power failure and thus blower failure, after that there is another manual valve before it enters the blower air flow. Once the gas and air are mixed it’s piped into the underside of the furnace housing where it “T”s off and comes out both sides. It enters the furnace chamber in two places one on either side at the top and bottom respectively, directing flow in a circular path around the inside of the furnace. The pilot / igniter is joined to the upper gas/air entrance to the furnace chamber.

    I still don’t understand the square block (chimney? Exhaust?) on the side and why it has the lower rectangular opening. What would it be for? What would happen if it were fired up as is with it open? Does it act as an up draft for the exhaust?

    thank you for your time and help!
  6. OMM

    OMM Silver

    The square block on the side is the exhaust. The draft hole allows more oxygen if the fuel is burning a bit too rich. It’s somewhat of an afterburner.
  7. thanks man!
  8. PatJ

    PatJ Silver

    With the furnace being pressurized with the blower, it would seem that the rectangular hole would need to be closed, else your exhaust gasses would just flow out that rectangular hole, and not go up the stack.

    Pressure will be relieved along the path of least resistance (out the rectangular hole).

    The only way I could see the rectangular hole working is if the stack was very tall, and had a significant draft to it.
    Even then, I don't think that would prevent hot gasses from coming out the rectangular hole.

    Another idea is that somewhere at then end of a long stack pipe is an exhaust blower, and creates a negative pressure on the box on the right side of the furnace.

    You are going to have to seal tightly the rectangular hole, else you are going to have very hot gases coming back onto the gas piping, etc., which is something to be avoided at all cost.
    Obviously this is subject to debate, but that is what I have observed from my experience.

    And there does appear to be regenerative pipes on both sides of the furnace, and I would guess they take hot gasses from the top of the furnace and redirect them to the bottom of the furnace.
    I think that because there are refractory blocks at the top of each vertical regeneration pipe, because the top of the pipe would be the very hot side.
    The lower part of the pipe may be at 1000 F or some temperature that would not require refractory around the pipe.

    A most interesting design.
    Just when you think you have seen it all, wammo, someone comes out of the woodwork with a new/old design.

    Just wait until ironsides sees this; there will be some spirited debate at that point.
    He is more opinionated than I am, but he would vigorously debate that point too.
    He does know an awful lot about all things foundry though, and it would be interesting to get his slant on this arrangement.

    I orginally thought there were two burner tubes entering the furnace down low, but with additional photos, I think the other horizontal object is the support for the burner tube, and so there is only one burner tube entering the furnace low on the right side.

    The exhaust is a little below the vertical centerline of the furnace.

    Last edited: Jan 27, 2020
  9. OMM

    OMM Silver

    Pat, I think you need to take a better look at the pictures and read what Brandon said in Post #4.

    There are two burners 180° apart one at the top of the furnace and one at the bottom of the furnace. The side exhaust hole exits the bottom of the furnace.

    Edit; a little oops on my behalf. 120,000 BTU. If it had a 4 to 6 inch chimney, I think it would naturally draft. Maybe at one point it did have a door and it was the clean out for the chimney.
    Last edited: Jan 27, 2020
  10. PatJ

    PatJ Silver

    I don't see that.
    I only see one burner tube entering the furnace on the lower right.

  11. OMM

    OMM Silver

    Red are the two torches, yellow is the internal exhaust port.
    2A5D008C-4C9E-41A6-90F8-DC9BB323069B.jpeg A808C150-9A81-454C-913A-0716312C2D0E.jpeg DADD37F0-AAD6-4293-BA8B-DE67BE0EB2D0.jpeg
    Last edited: Jan 27, 2020
  12. PatJ

    PatJ Silver

    Hmmmmmm..............................I don't see that at all.
    Well I have no doubt there will be some spirited discussion on this.

    And the acid test will be to fire it up (as Elmer Fudd would say "vewy cafuwy", ie: very carefully) !
    That will tell the story for sure.

    Just turn on the blower, and introduce a bit of non-combustible smoke (if there is such a thing) into the blower intake, without hooking it to natural gas, and the smoke will trace the path of the various burner and other passages.


  13. I have traced the pipes and burner passages, as I mentioned it enters the bottom of the furnace and into a “T” junction directing gas to either side of the furnace. I don’t have a photo of this because it’s happening under the furnace but is not enclosed in refractory. It is as OMM illustrated with the red arrows though.

    there doesn’t appear to have ever been a door on the rectangular hole and this was in service in a high school and I’m lead to believe it was functioning as is.

    I’m going to try to fire it up And see how it exhausts. Thanks guys! I’ll keep you posted.
    Last edited: Jan 27, 2020
  14. OMM

    OMM Silver

    Some see it, some don’t.

    I think you got yourself a good furnace, but it might need a little bit of repair.

    How is that lid removed? Is there a mechanism or is it a two-man with a bar through the U hole?
    Brendon Hartley likes this.
  15. PatJ

    PatJ Silver

    As John Denver use to say "like WOW man".
    Matt, I never doubted you for a second..........LOL, yes I did, I thought you had just gotten into some bad weed or something.
    I now unofficially dub OMM as "eagle-eye Matt".

    I see it now.
    I will have to ponder this further.
    I have seen a MIFCO furnace with stacked twin gas entries into the side of the furnace, one directly above the other, but never in my wildest dreams (limited imagination) would I suspect routing the gas lines under the furnace.

    It does make for a cleaner design, just hope the pipes don't rust out under there.

    Ironsides routinely shames me for my ignorance, so I am quite use to being wrong (he makes great sport of it). No pain, no gain as they say.
    I could not see the forest; there were too many trees in the way.

    The dual burner plumbing that I used on the outside of my dual burner furnace was way too big and long, and was a serious obstruction to trying to run the furnace.
    So I see why they would tuck the piping under the furnace.

    I asked one of my college professors if I could get partial credit on an exam question, and he said "You don't get partial credit for being wrong".
    What a party pooper that man was!

    Here is a picture of an externally plumbed dual burner MIFCO furnace.


    Last edited: Jan 28, 2020
    Brendon Hartley likes this.
  16. Petee716

    Petee716 Gold Banner Member

    Yeah having the plumbing underneath does keep the footprint down a bit. The afterburner setup with the rectangular hole is pretty interesting. It addresses one of the OP's comments about its proximity to the controls i.e. It only has cold air drawing in, not blowing out. It seems like there would be a better spot for it though. The airflow could actually provide for some cooling of that area I suppose. It looks like we'll find out!

    Brendon Hartley likes this.
  17. there is a lifting mechanism, I have it pulled off to repair it, the lifting cam is worn out so I’ll have to fab a new one. I’m going to redo some of the fittings and the electrical before firing it up but hopefully try it next week!

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